1. Field of the Invention
The present invention relates to a method and to bulk starter compositions for growing acid producing bacteria by using an essentially water insoluble or temporarily water insolubilized and thus initially solid form of a neutralizing agent in the growth medium which is adapted to provide a controlled reaction with the acid produced by the bacteria without substantially raising the pH of the growth medium. In particular, the present invention relates to a preferred method wherein the solid form of the neutralizing agent maintains a selected pH range in the growth medium by a controlled reaction of an insoluble form of the neutralizing agent over a period of time with the acid produced by the bacteria.
2. Prior Art
Encapsulating techniques and encapsulated products for the controlled release of materials as a function of the destruction of the encapsulating agent over a period of time are well known to the prior art. For instance, Gutcho, M. H., 1976. Microcapsules and Microencapsulation Techniques. Noyes Data Corp. Park Ridge, N.J. provides many examples of both.
In the field of microbiology, time-releasing capsules have been used to provide for the delayed controlled release of components of bacteriological media where identifying test reactions of the released components are required (Sveum, W. H. and P. A. Hartman, 1977. Appl. and Environ. Microbiol. 33:630-634; Lanz, W. W. and P. H. Hartman, 1976 Appl. and Environ. Microbiol. 32:716-722). They also have been used for the delayed release of nutrients in growing mushrooms (Carroll, A. D. and L. C. Schisler, 1976. Appl. and Environ. Microbiol. 31:499-593); for the delayed release of gluconic acid as an acidulating agent during the smoking of sausage (Rugala, W., 1978. Food Engineering 50:174); and, for incorporating ripening agents into cheese (Magee, E., Jr. and N. F. Olson, 1978. Proceedings 73rd Annual Meeting Am. Dairy Sci. Assn., p. 114).
In prior art unrelated to microbiology, methods and compositions for controlling pH by use of encapsulated alkaline or acid releasing materials are described for instance in U.S. Pat. No. 3,937,789 and in related U.S. Pat. Nos. which include 2,845,354; 3,133,862; 3,242,051; 3,622,350; 3,639,306; 3,792,171; 3,943,063; 3,949,094; 3,949,096; 3,952,110; 3,959,499; 3,976,794; 3,985,913; 3,996,156 and 4,004,039. This is also described in Food Product Development Vol 10 No. 6 pages 19 and 20 (July-Aug. 1976). These patents describe methods and materials which can be used in the present invention providing they are nontoxic to acid producing bacteria in the growth medium. The use of essentially water insoluble or temporarily water insolubilized neutralizing agents to control the pH in cultures of acid-producing bacteria has not been made by the prior art so far as is known.
It is well known to those skilled in the art that neutralization is very important to the growth of acid producing bacteria. The reason for this is that the acid produced impairs the bacteria and will eventually injure and kill them, especially at pH's of 5.0 and below. Thus it is a common practice to provide for continuous neutralization by the continuous addition of a water soluble base or basic aqueous solution such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, or ammonia gas so as to provide a pH which is neutral or slightly acid. Specialized equipment has been developed to monitor the pH of the growth medium and to add the neutralizing agent as needed. One patent describing this method is U.S. Pat. No. 4,021,304.
The present state of the art in growing bacteria to high cell counts for use as bacterial starters in preparing fermented dairy products such as cheese has been detailed recently (Sandine, W. E., (1977), J. Dairy Sci., 60:822-828; and Sandine, W. E., (1979), Lactic Starter Culture Technology. Pfizer, Inc., New York, New York). Numerous cheese plants in the U.S. are installing gaseous ammonia injection systems and pH recording devices in order to neutralize injurious acid produced during the growth of the bacteria. These systems, which are costly and require technical training to operate and maintain, have been described in a number of publications particularly Richardson, G. H., Dairy and Ice Cream Field 161(9):80A-80D (1978).